Our tester has produced the following:

Comment:

Post:

And the user page; note the size of the horizontal scrollbar:

We should probably prevent that from rendering like that. I think we do have a reasonable-ish limit on the length of user names, but special character encodings might be in play here. I'm not sure what limitations make sense; maybe we can instead truncate where necessary? Is that possible? Can we, in the UI, give an element a bounding box and say "you must fit within this space", so the rest of the page displays ok?